A ferromagnetic fluid is a liquid that becomes magnetized in the presence of a magnetic field. Ferromagnetic fluids can be used as passive components, such as seals, in which a ferromagnetic fluid is held in a fixed position by its attraction to a magnet. Ferromagnetic fluids can also be used as active components, such as valves, in which the ferromagnetic fluid changes position or configuration to open and close the valve controlled by an attraction between the ferromagnetic fluid and a magnet.